Outcrop and Subsurface Characterization of Carbonate Reservoirs for Improved Recovery of Remaining Hydrocarbons
The Reservoir Characterization Research Laboratory (RCRL) for carbonate studies is an industrial research consortium run by the Bureau of Economic Geology (BEG) and the Department of Geological Sciences of the John A. and Katherine G. Jackson School of Geosciences, The University of Texas at Austin (UT). RCRL's mission is to use outcrop and subsurface geologic and petrophysical data from carbonate reservoir strata as the basis for developing new and integrated methodologies to better understand and describe the 3-D reservoir environment.
With this proposal, we invite you to participate in the continuation of the RCRL Carbonate Reservoirs Research Program. A list of sponsors during 2007 can be found at the end of this proposal. In 2008 the annual RCRL Industrial Associates contribution to the program will continue to be $45,000 per year.
The RCRL program has run continuously since 1987 and has produced more than 45 external publications, as well as BEG publications, on carbonate reservoir characterization, sequence stratigraphy, petrophysics, geostatistics, and petroleum engineering. RCRL has maintained a membership of between 13 and 20 companies per year (see list of 2007 sponsors at end of proposal). The sponsorship currently is interested in a range of domestic and international carbonate reservoirs ranging in age from Ordovician to Cretaceous. This enrollment, supplemented by other grants, supports between three and six professional staff members and varying numbers of graduate student research assistants, as well as strong computer, editing, and graphics services.
Dr. Charles Kerans, Geology Professor, Principal Investigator
Mr. F. Jerry Lucia, Geological Engineer, Principal Investigator
Dr. Xavier Janson, Geologist
Dr. Christopher Zahm, Geologist
Mr. Jerome A. Bellian, Geologist
Dr. Fred Wang, Reservoir Engineer
Dr. Hongliu Zeng, Geophysicist
All staff members have extensive industry experience or have worked closely with industry and are well aware of the challenges and questions facing development geoscientists and engineers. We are also proud of our graduate student staff, which has included several award-winning students, many of whom are now working in industry.
Each year we combine industry input with our own ongoing research plans to develop a set of key geological and engineering research topics. Plans for 2008 focus on the following areas:
Geologic Characterization and Fluid Flow in Fractures and Nonmatrix Pore Systems
Outcrop Studies of Carbonate Heterogeneity Style—Platform, Slope, and Basin
Subsurface Reservoir Models and Modeling Methods
Seismic Imaging of Carbonate Heterogeneities
Rock Fabric, Petrophysical, and Predictive Diagenesis Studies
Our industrial sponsors will continue to receive research results at annual review meetings, in short courses, during mentoring activities, in publications and CD’s, and on our new developing, members-only RCRL database (http://begsql.beg.utexas.edu/rcrl/login.aspx). We have also released to all sponsors TexSim Version 2.0 hard drives, which contain outcrop-interpreted photopanels, geological models, field guides and papers (in PDF format), lidar models, measured sections, photomicrographs, geologic maps, and synthetic seismic lines contained in a geographically correct spatial/visual database. This technology transfer tool was developed by Statoil, KongsbergSim, and BEG for all study areas within Texas and New Mexico to aid in technology transfer from current, past, and future field projects.
Workshop and Field Course
In 2007 we conducted one reservoir modeling workshop and a field course for our sponsoring companies. We will design a new modeling workshop that is tentatively planned for spring 2008. We will send a more detailed program of the workshop early in 2008.
The scale and lateral variability that outcrop exposures provide the development geoscientist cannot be underestimated. The challenge in effective characterization of reservoirs lies in understanding the scales and complexities of depositional and structural heterogeneity. RCRL is therefore continuing to develop and improve upon its field-based characterization short course for sponsor companies. The 2008 course will be similar to that presented in 07, except that we will conduct the course in a chronological/tectonostratigraphic context, beginning with the cyclicity and karst development of the Lower Ordovician (greenhouse) passive margin and continue up through the lower Carboniferous transitional deeper ramp/buildup complexes of the precollisional Oro Grande Basin, the upper Carboniferous icehouse cyclic mounds of the syntectonic Oro Grande Basin, and the transitional ramps and rimmed margins of the Permian Basin in the Guadalupe Mountains. This course will illustrate both exploration and reservoir-scale stratal architecture and methodologies for interpreting these geometries from contained facies. Data examined will include outcrops, cores, and subsurface analog data. The course will also consist of field lectures and hands-on field exercises, such as mapping of lateral facies variations describing vertical and lateral cycle architecture and seismic-scale stratal geometries and methods for capturing fracture data, combined with evening discussions/lectures on methods of constructing 3D reservoir models using both outcrop and subsurface data.
RCRL has historically conducted short-term projects with specific companies to help transfer its research results into an industrial work flow. In 2007 we initiated such a project with Kinder Morgan on the Cisco Formation in an area of the Sacroc Northern Platform. Apache has also provided data from the Adair Wolfcamp Unit that is being studied by A. Wilson under the direction of Charlie Kerans. In 2008 we plan to assist Husky and Shell with their effort to characterize the large tar accumulation found in the Grosmont and Ireton (Devonian) Formations in Alberta, Canada.
Sponsors are encouraged to contact us with projects that could be mutually beneficial.
Research Program For 2008
Characterization of Fractures and Nonmatrix Pore Systems
Mechanical Stratigraphy within Cretaceous Carbonates
When present as a connected network, open fractures commonly dominate fluid flow in reservoirs and dictate the success or failure of secondary and tertiary development programs. Fracture development can be facies specific or confined within composite sequences that comprise mechanical units. Furthermore, fractures exhibit different attributes (e.g., orientation, intensity, and style) depending on the mechanical properties of the sedimentary facies within which they occur. Facies-bound fracture systems are problematic in the subsurface because they typically occur below seismic resolution and may be detected only in core and image logs. Their vertical extent, geometry, and genetic relationship to sedimentary facies must be understood to improve subsurface prediction and modeling. Field work will be done in several Lower Cretaceous outcrops in Texas to collect samples and map fracture distribution and characteristics, including mechanical properties of facies within a robust stratigraphic framework.
Fractures Associated with Stratigraphic Discontinuities, Sacramento and Franklin Mountains
Stratigraphic features such as carbonate mounds or karst breccias are associated with an apparent increase in fracture development, which in turn can be a productive element in subsurface reservoirs. Better characterization of fractures that develop in association with these features is required to assess their spatial distribution, frequency, timing, and fluid flow potential and to address challenges that they may pose for enhanced hydrocarbon recovery. Mississippian mounds that crop out in the Sacramento Mountains and collapse karst bodies that crop out in the Franklin Mountains represent two types of discontinuities that have an associated increase in fracture intensity. In 2008, fracture in these two areas will be characterized to quantify the intensity, orientation, and fracture style observed in these outcrops. Through this characterization, we hope to highlight relationships between fracture intensity and other geologic phenomena such as differential compaction, facies type, discontinuity shape, and distribution.
Facies to Flow Characterization of the Pipe Creek Analog
Geometry and distribution of intact rudist mounds and their associated debris facies are poorly characterized. In addition, fluid flow through large, connected pores common within these facies is difficult to quantify using standard simulation techniques. Since 2003, RCRL has been using the Pipe Creek outcrop as an analog for detailed mapping of spatial and vertical relationships of the mound core and debris and will continue characterization of this mound complex in 2008. The goal of this year's work is to build a 3D outcrop model that adequately captures observed facies heterogeneity. This work will be supported by acquisition of ground-penetrating radar and field mapping of facies using differential GPS. In conjunction with ongoing work supported by NSF, we will drill additional wells for tracer test studies. With these new wells we intend to collect down-hole GPR while performing cross-hole tomographic studies and circular VSP surveys for a better understanding of the challenges of geophysical characterization within large pore systems.
Franklin Mountain Karst Study
Strontium isotope ratios (87Sr / 86Sr) for host rock and breccias in the Southern Franklin Mountains will be examined for correlation along the lower Paleozoic 87Sr / 86Sr isotope curve. These data, in conjunction with biostratigraphic ages from conodonts extracted from breccia matrix, will be used to look for patterns within the breccia bodies. Stratigraphic modeling will continue utilizing existing measured sections, samples, and airborne lidar for the 20-km2 field area.
Outcrop Studies of Carbonate Heterogeneity Styles—Platform, Slope, and Basin
Channelization, Erosion, and Collapse of Reef-Rimmed Platform Margins
At what scale do large platform-margin collapse scars or reentrants influence slope and basin accumulation of reservoir-quality carbonate fan-channel complexes? What large-scale structures control the character of platform-margin and slope accumulations, their fracture patterns, and their compaction-driven geometries?
The various Permian shelf-to-slope systems as exposed in Guadalupe Mountain National Park are ideal for addressing issues related to large-scale stratal architectures of carbonate platforms and their relation to margin erosion and downslope export of sediment. In 2008 we will expand our earlier Wolfcampian and Leonardian studies to younger Guadalupian margins. Our goal is to use the range of Permian stratigraphic architecture to better understand the timing, mechanism, and architecture of these collapses and their influence on the nature, morphology, and distribution of deep-water, redeposited carbonate sediments.
We will continue our modeling in Shumard Canyon, where a wide range of slide scars, slumps, and bedrock submarine canyons can be mapped in 3D. Younger Permian margins also show erosion, reentrant, and margin collapse. In 2008, we will characterize and model these large-scale collapse features in 3D on the basis of outcrop along the Western Escarpment, Slaughter Canyon, Walnut Canyon, and Dark Canyon, while conducting reconnaissance in intervening canyons. These study areas will be integrated in a robust regional stratigraphic model built on DEM and airborne lidar data (see below).
Airborne Lidar Model of the Southern Guadalupe Mountains
3D analysis and reconstructions of the Capitan shelf-to-slope system as exposed in Guadalupe Mountain National Park is ideal for addressing structural and stratigraphic issues related to large-scale stratal architectures of carbonate platforms. An airborne lidar survey will be carried out with a helicopter-mounted unit shooting at a low or oblique angle, allowing effective capture of cliff faces and flatter surfaces. Airborne data collected in this way from the Guadalupe Mountains will allow us to work in digital 3D structure and stratigraphy at the platform scale, rather than at the flow-unit to local platform-margin scale associated with most of our models constructed using ground-based lidar?. We are still in the process of designing a regional survey and will soon take bids over a range of coverage areas of varying size during the winter and finalize the funding strategy by spring 2008.
Forced Regressive Depositional Patterns and the Origin of Sheetlike Grainstone Reservoir Facies in the Jurassic-Cretaceous
Many of the major Cretaceous and Jurassic carbonate-ramp reservoir units, such as the Arab D, Shuaiba and Thamama, contain widespread carbonate grainstones that appear to exceed dimensions predicted by study of any of our modern analogs. The origin of similar dip-continuous shore-parallel sand bodies in greenhouse systems like the Cretaceous Western Interior Seaway has been for a decade the subject of discussion in clastic literature. Laterally extensive carbonate grainstone bodies of the superbly exposed and tectonically quiescent Comanche Shelf provide an opportunity to document the architecture and petrophysical characteristics of these compound, laterally diachronous grainstone bodies. A combination of detailed facies and petrophysical characterization and digital mapping technology will be applied to improve our understanding of these grainstone systems and evaluate the relevancy of the forced regressive model for such deposits.
Two locations along the west and south margins of the Comanche Shelf provide excellent study areas for this analysis. Geological characterization of the Albian ramp in the Fort Stockton Embayment that was presented during the 07 field excursion will be a primary area of analysis in 2008. Initial work has shown that the upper Albian succession along and proximal to I-10 between Ozona and Bakersfield provides an almost continuous section from the landward side of the ramp crest to the intrashelf basinal area, especially for the latest cycles of the Albian 21 composite sequence.
This year's goals are to complete the regional stratigraphic architecture along this 80-km transect. We will focus on evidence of a diachronous origin of the capping grainstone complex and emphasize tools that might assist in subsurface analysis of such low-angle prograding systems. Investigations will include diagenetic changes along the profile that predictably affect reservoir quality. Because of the similarities between stratigraphic architecture and facies in this Albian Comanche Shelf system and the Aptian Shuaiba Formation reservoirs of the Middle East, we are planning to characterize petrophysical changes along the depositional profile in selected facies tracts.
The second area that will be part of this study is the Pecos River transect from Pandale to the Rio Grande. In this section, basic stratigraphic framework is already in hand, but the lateral continuity of the sequence-capping (possibly combined highstand/falling stage) grainstones is not well understood. Detailed evaluation of updip to downdip changes in the Albian 19 and 20 grainstones will complement studies along I-10.
Jurassic Outcrop Analog Reconnaissance
Several of the world's largest hydrocarbon reservoirs are contained within prograding Jurassic foreshore-shoreface systems, namely the Arab-D and Smackover. The subsurface of these reservoirs has been described, and a clear need for a better understanding of these facies associations has been identified. Potential outcrop study areas will be evaluated in 08 and presented for group evaluation during the October meeting.
Subsurface Reservoir Models and Modeling Methods
SACROC Northern Platform Cisco Study
In 2007 we began a reservoir study of part of the Northern Platform (NP) of SACROC (Pennsylvanian) field in the Permian Basin. The NP reservoir is divided into Canyon and Cisco strata, this study focusing on the complex stratigraphy of the Cisco. Integration of seismic and well log data showed a complex system of carbonate buildups on the west side of the NP and a more layered system on the east side. Analysis of extensive porosity and permeability data indicates that most of the facies have similar permeability, albeit slightly different porosity values. In 2008 we plan to integrate recent production data into the model and use flow simulation to test the similarity between simulated performance and actual production data.
South Texas Reservoir Study
In 2008 we will initiate a study of Cretaceous fractured and burial enhanced carbonate reservoirs in South Texas as part of our ongoing investigation into touching-vug reservoirs and the impact of burial dissolution on porosity and permeability development. This study is contingent on obtaining core, production, and seismic data from operating companies.
Modeling Carbonate Systems Using Multipoint Statistics
In collaboration with Dr. Sanjay Srinivasan of the U.T. Center for Petroleum and Geosystems Engineering, we have started a 3-yr research program to investigate how to apply multipoint statistic modeling methods to carbonate systems and reservoirs. The strength of multipoint statistics is that it is based on pattern recognition rather than a pixel-based variogram approach. We are hoping to integrate more a priori geological knowledge into this geostatistical technique by constructing both statistically and geologically meaningful training images for a range of carbonate stratigraphic architecture. Ultimately our goal is to develop algorithms and workflows that combine geostatistic and deterministic approaches to better guide our ability to model carbonate systems in subsurface. The initial focus will be on remodeling phylloid algal mound architecture in the Dry Canyon outcrop by building a training image that integrates the conceptual growth model of the mounds developed on the outcrop.
Seismic Imaging of Carbonate Systems
Lateral and Vertical Distribution of Seismic Properties in Carbonate Rocks
Using a new outcrop velocity device based on surface wave measurement, we will investigate vertical and lateral seismic velocity heterogeneity in carbonate rocks. Our plan is to investigate first the grainstone cycle in Lawyer Canyon, where RCRL has already collected detailed porosity and permeability and extensively analyzed the scale of petrophysical heterogeneities in the past. We will follow a similar acquisition and processing workflow so that we can compare scale and style of heterogeneity between these two rock properties that are difficult to relate. The goal of this study is not only to examine the potential covariance between seismic velocity and other petrophysical characteristics, but also to investigate the amount of small-scale heterogeneity that needs to be modeled in our synthetic experiment to render natural properties variation adequately.
GPR Study of Albian Cretaceous Rudist Mounds
In 2008, we will expand and compress our 2D GPR grid over Georgetown Lake spillway to map distribution and morphologies of the rudist mounds. In addition, a 3D GPR dataset will be acquired over one of the best-developed buildups to investigate the 3D architecture of these small (a few meters high and a few tens of meters wide) buildups. Additional 2D GPR surveys will be acquired in Pipe Creek and potentially in the Pecos River and Waco area mounds that will allow comparison of a range of rudist mounds in terms of rudist type, size, morphology, distribution, and architecture.
Seismic Imaging of Karst
In 2007, we began investigating the seismic response of various karst morphologies on the basis of modern karst features and various velocity models for the karstified zone. In 2008, we will continue this study by investigating and modeling in more detail velocity distribution in the karstified area. We will investigate the amount and style of seismic velocity heterogeneities in the paleokarst breccia in the Franklin Mountains. In addition, we will continue building 3D synthetic seismograms using modern karst features and combinations of modern karst features, as well as various velocity distribution scenarios.
Rock Fabric, Petrophysical, and Predictive Diagenetic Studies
Origin and Petrophysics of Limestone Rock Fabrics
In 2006 we initiated a detailed study of the diagenesis and petrophysics of limestones, which included investigations into intragrain microporosity and complex grain-dominated fabrics. The study concluded that most of the complex limestone fabrics can be attributed to conversion of aragonite grains and crystals to LMC and subsequent grain crushing due to overburden pressure. In addition, we now have data showing that modern carbonate grains (ooids and Halimeda) have 17 to 21% porosity, suggesting that the porosity within ooids and other skeletal grains is inherited and not formed by burial dissolution. In 2007 this study was broadened to include the concept of increase in porosity through burial dissolution. In 2008 we will continue to investigate the impact of burial dissolution on the porosity and permeability of limestones and to measure the porosity of modern skeletal fragments.
Capillary Pressure Models
In the past we have been unable to develop a general capillary pressure model that integrates rock fabric information owing to the lack of sufficient capillary pressure data with fabric information. However, we have acquired considerable new information over the past few years and think that renewed effort is warranted. In 2008, therefore, we plan to construct a general capillary pressure model using the concept of “rock-fabric number” instead of the “k/phi” term used in the Leverett J model. The advantage of the rock-fabric number is that it provides a closer link to the geologic model than does the k/phi term.
For the past several years RCRL has supported student research on modeling dolomitization by hypersaline reflux. Current research focuses on modeling dolomitization of the extensive San Andres (Permian) outcrop located on the Algerita Escarpment, Guadalupe Mountains, New Mexico. The outcrop, 1,500 ft high and over 50 miles long, has an equivalent subsurface section some 50 miles downdip and along depositional strike. In 2007 the initial flow model was completed on the basis of facies-derived petrophysical parameters. The model has a series of time steps that are based on a sequence stratigraphic model. Results are encouraging, and in 2008 we plan to construct a more detailed petrophysical model and focus on reactive transport modeling.
Currently RCRL has two databases, both of which contain georeferenced information. One is more global in reach and has online query capability (http://begsql.beg.utexas.edu/rcrl/login.aspx).
The second, more of a visual/spatial database restricted to Texas and New Mexico, was distributed on a USB removable hard drive to each company at the annual meeting. Updates to both of these databases are planned biannually. These are in addition to our Industrial Associates webpage (http://www.beg.utexas.edu/indassoc/rcrl/index.htm), which contains web-accessible copies of annual meeting summaries and annotated PowerPoint® talks.